In order to rotatably support with reference to the suspension the non-driven wheels that are supported by the suspended-type independent suspension for an automobile, various kinds of rolling-bearing units for road wheel have been used in which the outer ring and hub rotate freely by way of rolling members in combination.
In this kind of rolling-bearing unit for road wheel, the outer ring, which does not rotate even when in use, has a first installation flange around its outer peripheral surface for connecting it to the suspension, and an outer ring raceway around its inner peripheral surface.
In addition, the hub, which rotates when in use, has a second installation flange around its outer peripheral surface on a portion closer to the axially outer end (the term "axially outer" means the side toward the outside in the width direction of the automobile when installed in the automobile) and an inner ring raceway formed around its middle portion directly or by way of an inner ring.
Moreover, by placing the rolling members between the outer ring raceway and inner ring raceway so that they rotate freely, the road wheel that is fastened to the hub is supported rotatably with respect to the suspension to which the outer ring is fastened.
In the case of the rolling-bearing unit for road wheel used for supporting the non-driven wheels in this way, the hub does not particularly require a through hole that penetrates its center section and thus can be made solid.
On the other hand, in the case of a rolling-bearing unit for road wheel that is used for rotatably supporting the driven wheels {the front wheels for a FF vehicle, rear wheels for a FR and RR vehicle and all four wheels for a 4WD vehicle (four-wheel drive vehicle)} with respect to the suspension, it is necessary to connect the shaft of the constant velocity joint with the hub to which the road wheels are fastened. Accordingly, generally a through hole is formed in the hub through which the shaft is inserted.
Furthermore, as shown in FIG. 1, a rolling-bearing unit for road wheel used for supporting the non-driven wheels has been known and has actually been used. This construction uses common components for the rolling-bearing unit for road wheel for both the driven wheels and the non-driven wheels.
The outer ring 1, which does not rotate when installed in the vehicle and supported by the suspension, has a first installation flange 2 around its outer peripheral surface for supporting it by the suspension, and double rows of outer ring raceways 3 around its inner peripheral surface, respectively.
A hollow cylindrical-shaped hub 4 and inner ring 5 are located on the inside of the outer ring 1 and rotatable during use. Of these, the hub 4 has a second installation flange 6 around its outer peripheral surface on the axially outer end (left end in FIG. 1) for attaching it to the road wheel, and a first inner ring raceway 7a in its middle portion, as well as a through hole 8 that penetrates its center in the axial direction. Also, a second inner ring raceway 7b is formed around the outer peripheral surface of the inner ring 5, and the inner ring 5 is fitted around the outer peripheral surface on the axially inner end of the hub 4 (the term "axially inner" means is the side toward the center in the width direction when mounted on the automobile, the right in FIGS. 1 thru 14, and the left in FIG. 2).
A bolt 9 is inserted through the inside of the through hole 8, and a nut 10 is fastened to the tip end of this bolt 9 that sticks out from the axially outer end of the hub 4, and by tightening it securely, the hub 4 and inner ring 5 are held between the head 11 of the bolt 9 and the nut 10 such that the hub 4 and inner ring 5 are joined together as one body.
In addition, multiple rolling members (balls) 12 are placed between the outer ring raceways 3 and the inner ring raceways 7a, 7b such that they can roll freely.
Moreover, a short, cylindrical shaped cover 14 with a bottom, that is also referred to as a first seal member in the present specification, is formed by bending sheet metal and attached to the opening on the axially inner end of the outer ring 1.
Together with this, a seal ring 13, which is also referred to as a second seal member in this specification, is located between the opening edge on the axially outer end of the outer ring 1 and the outer peripheral surface in the middle portion of the hub 4. These seal members prevent foreign matter such as mud, dust, dirt and the like from getting inside the space 15 where the rolling members 12 are located, and they also prevent lubrication grease that is in this space 15 from leaking out.
When the rolling-bearing unit for road wheel that is constructed as described above is being used, the first installation flange 2 that is formed on the outer ring 1 is fastened to part of the suspension (not shown in the figures) and the second installation flange 6 that is formed around the hub 4 is fastened to the non-driven wheel (not shown in the figures).
When the rolling-bearing unit for road wheel supports the non-driven wheel as shown in FIG. 1, it is possible to make the hub common with the rolling-bearing unit which supports the driven wheel. In other words, as mentioned above, in the case of a general rolling-bearing unit for road wheel which supports the driven wheel, it is necessary to have a hole (this is generally a spline hole) through the center of the hub through which the constant velocity joint can pass.
As to this hole, with the construction shown in FIG. 1, there is a through hole 8 through the center of the hub 4, so that there is no need to make a separate hole in the hub because of the existence of this through hole 8. The through hole 8 in the hub 4 for the non-driven wheel can be used as is before forming a spline, and thus it is possible to keep down the rising costs that accompany the formation of a spline.
In the case of the construction shown in FIG. 1, since the opening on the axially inner end of the through hole 8 is sealed tight by the bolt 9 and nut 10, it is possible to prevent the lubrication grease in the space 15 from getting inside this through hole 8, and thus it is not necessary to increase the amount of grease used.
Moreover, a rolling-bearing unit for road wheel as shown in FIG. 2 has been disclosed in U.S. Pat. No. 3,589,747. In the case of this rolling-bearing unit for road wheel, a hollow, cylindrical shaped hub 4 and the inner ring 5, which is fitted around the hub 4 on the axially inner end (left side in FIG. 2), are supported on the inside of the outer ring 1 by a tapered roller bearing such that they can rotate freely with respect to the outer ring 1. Therefore, a pair of tapered concave shaped outer ring raceways 54 are formed around the inner peripheral surface on both ends in the axial direction of the outer ring 1 such that they are tapered in opposite directions. Moreover, tapered convex shaped inner ring raceways 55a, 55b are formed around the outer peripheral surface in the middle portion of the hub 4 and around the outer peripheral surface of the inner ring 5, respectively, such that they are tapered in opposite directions.
Also, multiple tapered rollers 56 are located between the outer ring raceways 54 and the inner ring raceways 55a, 55b such that they can roll freely.
Furthermore, in the case of the construction shown in the figure, in order to fasten the inner ring 5 to the axially inner end of the hub 4, a plastically deformed section 58 that sticks out in the radial direction toward the outside is formed on the axially inner end of the hub 4. The inner ring 5 is held between this plastically deformed section 58 and a stepped section 59 that is formed around the outer peripheral surface in the middle portion of the hub 4.
Moreover, a short, cylindrical-shaped cover 14 with a bottom, which is also referred to as a first seal member in this specification, is formed by pressing sheet metal and attached to the opening on the axially inner end of the outer ring 1. Together with this, a seal ring 13, that is also referred to as a second seal member in this specification, is placed between the opening on the axially outer end (right end in FIG. 2) of the outer ring 1 and the outer peripheral surface in the middle portion of the hub 4. Furthermore, a through hole 8 is formed such that it penetrates through the center of the hub 4 in the axial direction and a seal member 57 is attached to the inner peripheral surface of the axially inner end of the through hole 8 and this seal member 57 seals the axially inner end of the through hole 8.
In the case of the construction disclosed in U.S. Pat. No. 3,589,747 and described above, the construction differs from that shown in FIG. 1 in that there is no need to insert a member such as a bolt 9 (see FIG. 1) through the inside of the through hole 8 formed in the hub 4. Also, since the seal member 57 is formed on the axially inner end of the through hole 8, it is possible to prevent the lubrication grease in the space 15 where the tapered rollers 56 are located, from getting into the through hole 8, and thus it is not necessary to increase amount of grease used.
In recent years, from the aspect of improvement in performance of automobile fuel efficiency, comfort, and dynamic power, there has been an increasing demand for lighter rolling-bearing units for road wheel. As a means for making it possible to lighten the rolling-bearing unit, removing any unnecessary material in structure from the hub of the rolling-bearing unit, which supports the non-driven wheels, has been effective. Accordingly, forming a through hole in the hub not only for the rolling-bearing unit which supports the driven wheels, but also for the rolling-bearing unit which supports the non-driven wheels is desired in order to lighten the weight of the automobile.
On the other hand, as shown in FIG. 1, construction for actually removing material from the hub 4 by forming a through hole 8 in the hub 4 has been formerly considered, however, this was performed simply from the aspect of making the bearing common for all wheels. Also, in the construction of bearing shown in the same figure, part of a bolt 9 is inserted through the through hole 8, so that it is not really possible to effectively lighten the weight of the bearing.
Conversely, in the case of the construction disclosed in U.S. Pat. No. 3,589,747 as shown in FIG. 2, no members, such as a bolt, that would increase the weight of the bearing are inserted through the through hole 8 in the hub 4. Therefore, the construction shown in FIG. 2 differs from that shown in FIG. 1 in that it can be effectively lightened, however, in the case of the construction shown in FIG. 2, there is no covering member on the axially outer end of the through hole 8, so that there is a possibility that mud or the like could get into the through hole 8 from the outside. If mud or the like gets inside the through hole 8, there is a possibility that the inner peripheral surface of the through hole 8 could rust, which would lower the durability of the hub 4.
On the other hand, construction that is different from the construction shown in FIG. 2 is also disclosed in U.S. Pat. No. 3,589,747, in which a through hole is formed that penetrates through the center of the hub in the axial direction and where its outer end is covered by a seal member (see FIG. 6 of the patent), but its inner end is not covered. With this construction, the problems that occurred in the construction shown in FIG. 2 do not occur. However, in the case of this construction, there is no seal member for covering the inner end of the through hole. Therefore, in the case of this construction, there is a possibility that the grease in the space where the rolling members are located could get inside the through hole, and in order to make sure there is always enough grease in this space, it is necessary to increase the amount of grease that is filled into the space. Increasing the amount of grease in this way increases the cost and weight of the rolling-bearing unit for road wheel, which is not desired.